1. Field of the Invention
The present invention relates to a support mechanism for an optical block having an optical head in an optical disc drive apparatus which performs writing and/or reading of signals carrying information with respect to an optical disc, an optomagnetic disc, or other disc-like recording media.
2. Description of the Related Art
In the past, there have been optical discs, opto-magnetic discs, and other disc-like recording media. Proposal has been made of an optical head which performs the writing and/or reading of signals carrying information by irradiation of a beam of light on these disc-like recording media.
A disc apparatus comprised so as to enable recording and/or reproduction of information signals on and/or from the above-mentioned disc-like recording media using such an optical head is provided with a support mechanism for an optical block having the optical head so as to enable the beam of light emitted from the optical head to be irradiated perpendicularly with respect to the signal recording surface of the disc-like recording medium and also to enable the optical head to be moved and operated across the inner and outer circumferences of the disc-like recording medium.
For such a support mechanism, in the past, as shown in FIG. 1 and FIG. 2, proposal has been made of a mechanism wherein a plurality of rollers 53, 54, 55, 56, 57, 58, and 59 are rotatably attached to an optical block 52 having an optical head 51 where an object lens 51a etc. are held, these rotatable rollers 53, 54, 55, 56, 57, 58, and 59 are made to abut against a reference shaft 60 and a support shaft 61 arranged in parallel set apart a predetermined distance from each other, and thus the optical block 52 is supported between the above-mentioned shafts 60 and 61 in a manner enabling movement in the axial direction of the reference shaft 60.
In the above-mentioned support mechanism, among the above-mentioned plurality of rollers 53, 54, 55, 56, 57, 58, and 59, the two pairs of rollers 53, 54 and 55, 56 abutting against and so as to grip the reference shaft 60 are attached rotatably to one side of the optical block 52. Further, the remaining rollers 57, 58, and 59 abutting against the support shaft 61 are rotatably attached to the other side of the optical block 52. The rotating roller 57 is provided at the side of the optical block 52 where the optical head 51 is. At the opposite side of the above-mentioned optical block 52 where the optical head 51 is not present, at the bottom in FIG. 1, a pair of rollers 58 and 59 which abut against so as to grip with the rotational roller 57 the support shaft 61 are attached rotatably to L-sectional shape plate springs 62 and 63 attached to the optical block 52. In the plate springs 62 and 63, the base portions 62a and 63a are affixed by setscrews etc. to the optical block 52, while the tip portions 62b and 63b are made to elastically deform in the direction shown by the arrow a in FIG. 1, so a gripping pressure is caused on the support shaft 61.
Therefore, in the support mechanism, the rollers 58 and 59 attached to the plate springs 62 and 63 are pressed to the support shaft 61 side by the elastic force of the plate springs 62 and 63. By the counteraction of this, the optical block 52 is elastically biased to the reference shaft 60 side, whereby the optical block 52 is positioned based on the reference shaft 60.
Further, as another conventional support mechanism, as shown in FIG. 3 and FIG. 4, there has been proposed a mechanism wherein a plurality of rollers 76, 77, 78, 79, 80, and 81 are attached rotatably to an optical block 52 having an optical head 51 where an object lens 51a etc. are held, these rotating rollers 76, 77, 78, 79, 80, and 81 are made to abut against the reference shaft 60 and support shaft 61 which are disposed in parallel with each other set apart by a predetermined distance, and the optical block 52 is supported between the two shafts 60 and 61 in a manner movable in the axial direction of the reference shaft 60.
That is, in the above support mechanism, two pairs of positioning rollers 76, 77 and 78, 79 are attached in the front and rear of the optical block 52 in the direction of travel thereof shown by the arrow T in FIG. 4. These pairs of positioning rollers 76, 77 and 78, 79 are provided rotatably at one side of the optical block 52.
On the other hand, at the other side of the optical block 52 opposite to the side of attachment of the positioning rollers 76, 77, 78, and 79, there is attached a roller support member 82 for pressing the pair of pressure rollers 80 and 81 to the support shaft 61.
The roller support member 82, as shown in FIG. 3, is comprised of a roller holder 83 for attaching the pair of pressure rollers 80 and 81 and a holder support member 84 for supporting the roller holder 83.
The holder support member 84 is for pressing the pair of pressure rollers 80 and 81 attached to the roller holder 83 to the support shaft 61. For example, it is formed from a spring material comprised of a metal sheet etc. and so as to have a U-sectional shape. It has a pair of convex portions 86 and 87 and has a flat surface elastic displacement portion 88 which projects slightly toward the roller holder 83 side. The elastic displacement portion 88 is such that when the holder support member 84 is attached to the optical block 52, the pair of convex portions 86 and 87 abut against the side surface 52a of the optical block 52 in linear contact, so elastically displaces in a direction (the arrow X direction in FIG. 3) substantially perpendicular to the axial direction of the support shaft 61 using the convex portions 86 and 87 as support points. Therefore, the pair of pressure rollers 80 and 81 attached to the roller holder 83 are disposed so as to abut so as to grip the support shaft 61 by the peripheral surfaces of the pressure rollers 80 and 81. Further, at this time, the elastic displacement portion 88 provided at the holder support member 84 is elastically deformed to the side close to the optical block 52, so the elastic displacement portion 88 presses the pressure rollers 80 and 81 against the support shaft 61 in a direction substantially perpendicular to the axial direction of the support shaft 61 shown by the arrow X direction in FIG. 3, so due to the counteraction, the optical block 52 is elastically biased to the reference shaft 60 side and therefore the optical block 52 is positioned based on the reference shaft 61.
However, in the support mechanism as shown in FIG. 1 and FIG. 2, the reference shaft 60 and the support shaft 61, which are disposed in parallel with each other set apart by a predetermined distance, ideally have a constant distance between the two shafts, that is, shaft pitch, across the entire path of travel, but there is some fluctuation of the shaft pitch due to the mechanical precision at the time of arranging the shafts 60 and 61, the precision of the shafts themselves, the pressure applied by the plate springs 62 and 63, etc.
Therefore, among the rollers 57, 58, and 59 abutting so as to grip the support shaft 61, only the rollers 58 and 59 have been made to elastically biased to the support shaft 61 by the plate springs 62 and 63, so as shown in FIG. 5, the optical block 52 ends up slanted from the state shown by the broken line to the state shown by the solid line by the amount by which the distance (P) of the shafts becomes smaller than the predetermined value. That is, rotational motion (below called "rolling") about the direction along the direction of travel of the optical block 52 occurs and the optical block 52 slants. Therefore, it becomes impossible to irradiate an accurate light beam to the signal recording surface of the disc-shaped recording medium from the optical head 51 provided at the optical block 52.
Further, in the conventional support mechanism shown in FIG. 3 and FIG. 4, even if the shaft pitch between the reference shaft 60 and the support shaft 61 changes, the roller holder 83 of the pressure rollers 80 and 81 moves only in the arrow X direction in FIG. 3, so rolling of the optical block 52 such as shown by R in FIG. 3 can be avoided. However, even in this support mechanism, the optical block 52 is constructed to only grip one location of the support shaft 61 in the axial direction by the pressure rollers 80 and 91 at the other side, so when the optical block 52 travels in the front-rear direction of the two shafts 60 and 61 shown by the arrow T in FIG. 4, the phenomenon is discovered of vibration upward and downward in the direction shown by the arrow Y in FIG. 4 around near the location of gripping by the pressure rollers 80 and 81. It was found that there was a problem of the optical head 51 attached to the optical block 52 being affected by this, whereby the optical axis of the object lens 51a fluctuated. This is believed to be caused from the mechanical resonance system of the drive and support structure as a whole, comprised of the support of the optical block 52 with respect to the reference shaft 60 and the support shaft 61 and the mechanism of movement of the optical block 52, the linear motor 87 etc.